E3S Web of Conferences 272, 01013 (2021) https://doi.org/10.1051/e3sconf/202127201013 ICEPG 2021 Life cycle carbon emission of monorail transit and its comparison in operation stage with other city transit modes Teng Li1, Eryu Zhu1*, Haoran Liu1 1Dept. of Civil Engineering., Beijing Jiaotong University., Shangyuancun 3rd, Beijing, China, 100044 Corresponding author, Eryu Zhu, Professor of Bridge Department, Beijing Jiaotong University, Ph. D, China. Abstract. In this paper, carbon emissions of a monorail transit are calculated using the method of whole life cycle, which can be divided into four stages: material manufacturing stage, construction stage, operation stage and demolition stage. In the operation phase, the units are PKT (Passenger Kilometers Travelled) and VKT (Vehicle Kilometers Travelled), while in other three stages, the unit is 1 km. The results show that the carbon emissions from the 1km length monorail are 6271.204 tons. In addition, in the operation stage, it is found that the PKT index and VKT index of Chongqing monorail transportation are 0.07468 and 3.31933 respectively, far lower than those of subways in the same city. For PKT indicators of other rail transits, from small to large, they are light rail, tram, subway, APM and maglev. As for VKT indicators, from small to large, they are tram, light rail, subway, APM and maglev. The PKT index of Beijing subway is the lowest compared with that of other cities. subway, maglev, APM and trams, to find a lower carbon 1 Introduction emission transit mode, and to facilitate the adjustment of In recent years, with the continuous increase of urban the urban rail transit system and urban sustainable population density, the flow of people and goods between development, and to provide suggestions for government cities and the construction of rail transit are in full swing. policies. However, with the continuous expansion of the construction scale of different types of rail transit, the 2 Whole life cycle carbon emission topic of environmental pollution, which is closely related to the life quality of residents, begins to receive the close The carbon emission calculated in this paper is based on attention of the country and the society. The increasing the method of whole life cycle, and the carbon emission carbon emission has posed a threat to human lives in the of different traffic projects is divided into the following world. In this year, the concept of carbon neutrality and four stages: material manufacturing stage, construction carbon peak was first written into the government work stage, operation stage and demolition stage [3]. The report in China [1]. Carbon peak means that China corresponding list is established for each stage, and carbon promises that carbon emissions will stop growing by 2030 emissions of each item in the list are calculated. The and gradually decline after they peak. Carbon neutrality carbon emissions of the whole life cycle are obtained by means that enterprises, groups or individuals calculate the summing up the carbon emissions of the four stages. total amount of greenhouse gas emissions directly or indirectly generated within a certain period of time, and then offset the carbon emission generated by themselves 2.1. Carbon emission calculation methods in through plant afforestation, energy conservation and each stage emission reduction, etc., so as to achieve the goal of zero The calculation method of carbon emission in each stage emission. [4] is as follows. According to statistics [2], carbon emission from In the material manufacturing stage, the following China's transportation industry accounts for nearly 10% of formula is used: China's total carbon emissions. And with the advancement (1) of urbanization and industrialization, the carbon emissions from China's transportation industry will is the carbon emission in the production and continue to increase. Therefore, the development of green transportation has a very great significance. However, processing stage of building materials; is the there has been little analysis of the carbon emissions of consumption of the ith material in the production and different modes of transport. In this paper, carbon processing stage of building materials; is the carbon emissions from different urban transit modes are emission of the production process of unit building calculated and compared, including monorail transit, materials. *[email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). E3S Web of Conferences 272, 01013 (2021) https://doi.org/10.1051/e3sconf/202127201013 ICEPG 2021 In the construction stage, greenhouse gas emissions is the carbon emission in the demolition stage; mainly come from the transportation of materials and is the amount of the ith material in the construction stage; different construction works, and results are related to the is the carbon emission per unit transportation distance transportation distance of building materials and the of the vehicle; is the transportation distance. is the amount of works in each process. The following formula amount of works in each process in the demolition stage will be used to calculate carbon emissions in the and is the carbon emission generated by unit work in construction stage: each process. (2) is the carbon emission in the construction stage; 2.2. Carbon emission factors is the amount of the ith material in the construction stage; Energy consumption carbon emission factor refers to the is the carbon emission per unit transportation distance of the vehicle; is the transportation distance. is the amount of greenhouse gases associated with the consumption of unit mass energy, and is an important amount of works in each process in the construction stage parameter representing the characteristics of greenhouse and is the carbon emission generated by unit work in gas emissions of a certain energy type [5]. Carbon each process. emission factors of IPCC 2006 [6] are used in this paper. In the operation stage, energy consumption mainly The carbon emission factor of diesel is 3.16 kg CO2 / kg. comes from the electricity consumed during vehicle The average carbon emission factor of electricity operation, while carbon emission mainly comes from production in China is 1.062 kg CO2 / kilowatt-hour [7]. electricity production. The following formula is used to According to some research results [8-10], carbon calculate carbon emission in this stage: emission from C40 concrete is 644.59 kg/m3; carbon (3) emissions of 1-ton large size steel, medium and small size steel and steel wire are 20344.4 kg/ton, 16883.7 kg/ton, is the carbon emission in the construction stage; 16706.3 kg/ton, respectively. is the electricity consumed during operation in the life Carbon emissions in different works are mainly from cycle of different urban transit modes, and is the carbon the electricity consumption and diesel consumption from emission generated by production of unit electricity. various construction machinery and equipment. Carbon In the demolition stage, the following formula is used emission of concrete construction process per unit volume to calculate carbon emission: [11] is shown in the following table: (4) Table 1. Carbon emission of concrete construction per unit volume. Procedure（kg / m3） CO2 NOX Carbon Equivalent Template Works 46.975 0.377 159.321 Steel Works 13.947 0.427 141.193 Concrete Works 3.166 / 3.166 Earth Works 8.89 / 8.89 materials such as concrete and steel are considered. It is assumed that the average transport distance of steel is 2.3. Carbon emission from material 60km, and the transport distance of waste concrete is transportation 30km. In the material transportation process, carbon emissions are mainly caused by the energy consumed by 3 Estimation of life-cycle carbon transportation vehicles. Road transportation is the most common solution and the fuel of road vehicle is mainly emissions from monorail transit diesel. In this paper, the specific assumptions for material In this paper, 1km is selected as a functional unit to carry transportation are as follows: for concrete, 8 square out a theoretical analysis of carbon emissions of monorail concrete mixers are used, and the fuel consumption per transit in the four stages. A monorail transit line in China 100 km is 35L. As for other building materials such as is selected for analysis. The cross section of concrete PC steel, 20-ton freight vehicles are used, and the fuel guideway running by the train is I-shaped, 850mm wide, consumption per 100 km is 30L. It is assumed that the and 1.5m high. The structure is shown in the figures below round-trip transport distance of concrete is 30km, that of [12]: steel is 60km and that of earthwork is 15km. In the structural demolition stage, only the removal of major 2 E3S Web of Conferences 272, 01013 (2021) https://doi.org/10.1051/e3sconf/202127201013 ICEPG 2021 Figure 1. Cross section of monorail guideway Figure 2. T –shaped pier of monorail. Assuming the length of a span is 25 m and the bridge row of three piles, with diameter of each pile 100 cm. pier height is 9 m. There are 41 piers in 1 km length bridge Assuming the depth is 12 m. The volume of concrete or and the concrete volume of two guideways, 41piers, 41 earth is 1158.66 m3. Assuming the pile reinforcement ratio cover beams are 1912.8 m3, 1066.4 m3 and 598.477 m3, is 0.2%, then the steel quantity is 18190.96 kg. respectively. Assuming the C40 concrete and 10 bunches In all, total concrete volume is 4736.36 m3. Total of 3 - 7 Φ 5 steel strands are used in the guideway. Total quantities of steel rebar and strand are 74360.49 kg and steel strand volume in 1 km guideway is 8.2 m3.